Method for determining the purity of recovered sylvite

ABSTRACT

A method for determining the purity of recovered sylvite by taking an infrared spectrum of the sylvite and making up a calibration curve from known standards of a known impurity on the sylvite. The impurity peaks appearing in the infrared spectrum are then compared with the calibration curve and the impurity concentration of the sylvite is determined.

United States Patent Inventor Herbert H. Defriez Berkeley, Calif.

Appl. No. 33,447

Filed Apr. 30, 1970 Patented Dec. 28, 1971 Assignee Shell Oil CompanyNew York, N.Y.

METHOD FOR DETERMINING THE PURITY OF RECOVERED SYLVITE 3 Claims, 4Drawing Figs.

Int. G01n 21/00 Field of Search 250/435 R,

[56] References Cited UNITED STATES PATENTS 3,109,932 11/1963 Spitzer250/833 H 3,511,570 5/1970 Mogayzel et a1.. 250/435 R X 3,205,355 9/1965Ehlert 250/833 11 X 3,351,757 11/1967 Fraseret a1. 250/833 H PrimaryExaminerArchie R. Borchelt Attorneys-T. E. Bieber and J. H. McCarthyPATENTEU [H5828 1971 SHEET 1 [)F 2 FIG ..2

2 B 4 I l O 0 OPTICAL ABSORBANCE INVENTOR HERBERT H. DeFRIEZ M; W ,h 2/

FIG 4 ATTORNEYS PATENIEn uEmmn 3331.246

sum 2 or 2 q'po r k SAMPLE 3B SAMPLE 3A SAMPLE 2A 31l DILUTION l lDILUTION NOT DILUTED INVENTOR. V HERBERT H. DeFRlEZ FIG 3 am omuzvsMETHOD FOR DETERMINING THE PURlTY OF RECOVERED SYLVITE BACKGROUND OF THEINVENTION 1 Field of the Invention The invention relates to the purityof materials; and, more particularly, to a method for determining theconcentration of an impurity, such as a hydrocarbon, in recoveredsylvite.

2. Description of the Prior Art Water-soluble solids, such as sylvite,can be conveniently and economically transported over great distancesthrough pipelines as heavy suspensions in oily or hydrophobic fluids,such as crude oil or distillates. Recovery of the solid sylviteparticles at the receiving end will in some cases be via transfer of thesolid particles to an aqueous phase or other suitable methods, such as,for example, the methods described in a copending patent application toJune et al., Ser. No. 654,416, filed July 19, 1967, and in a copendingpatent application to Cheney, Ser. No. 725,053, filed Apr. 29, 1968.After such recovery, it is desirable to know the concentration ofhydrocarbon in the recovered sylvite. In the past, conventionalextraction methods have been used to obtain such information. However,such extraction methods are generally slow, inaccurate and notreproducible. One such extraction process used on recovered sylvite isthe toluene extraction method adapted from the International Mineralsand Chemical Corporation method for ether extraction of sylvite. Anotherprior art process used on recovered sylvite is the benzene extraction ofa solution of the contaminated sylvite in water. However, in oneexperiment using both aforementioned prior art processes, oil contentsapproximately 50 percent lower than values determined by conventionalcarbon-hydrogen analysis of similar samples were obtained. These lowvalues resulted from the evaporation step of the aforementionedextraction processes wherein lower boiling components were stripped fromthe extracted crude oil. Thus, such prior art processes are unsuitablefor quick and accurate determinations of the hydrocarbon content ofrecovered sylvite.

SUMMARY OF THE INVENTION It is an object of this invention to provide amethod for determining the purity of a material.

It is a further object of this invention to provide a method fordetermining the purity of recovered sylvite.

It is a still further object of this invention to provide a method fordetermining the purity of sylvite recovered from a slurry of an oil,such as crude oil.

These and other objects are preferably accomplished by taking aninfrared spectrum of the sylvite and making up a calibration curve fromknown standards of a known impurity on the sylvite. The impurity peaksappearing in the infrared spectrum are than compared with thecalibration curve and the impurity concentration of sylvite isdetermined.

Preferably, the sample is in the form of a relatively thin disc pressedfrom the sylvite, and the known impurity is a hydrocarbon with thecalibration curve being made up using a peak corresponding to thecarbon-hydrogen stretch bands at approximately 3.4 microns wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofapparatus for carrying out the techniques of my invention;

FIG. 2 is a vertical sectional view, similar to FIG. 1, showing afurther step in carrying out my invention; and

FIGS. 3 and 4 are graphical illustrations of the technique of myinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the invention will bedescribed hereinbelow with respect to determining the concentration ofcrude oil on recovered sylvite (i.e., KCI), the techniques describedherein are applicable to the determination of any impurity on sylvitethat has an infrared spectrum. Further, these techniques are alsoapplicable to the determination of the concentration of an impurityhaving an infrared spectrum in any material as long as the infraredabsorption lines of the material do not interfere with the infraredabsorption lines of the impurity.

It has been found that pure sylvite (i.e., pure RC1) is transparent toinfrared radiation between 1 and 15 microns wavelength. If any impurity,such as crude oil, is present on the sylvite, characteristic impuritypeaks, such as hydrocarbon peaks, will be present in an infraredspectrum taken of a sample, such as a relatively thin disc, pressed fromthe contaminated sylvite. A calibration curve is made up correspondingto the type of crude oil and sylvite comprising the sample. Sincedifierent crude oils and sylvites have different spectra, separatecalibrations must be made for each. However, assuming a sample of crudeoil and sylvite, because of its strong absorption and because sylvitehas no peaks in this region, the carbon-hydrogen stretch band, atapproximately 3.4 microns, may be used to make up a calibration curvefrom known standards of oil on sylvite. The percent by weight oil onsylvite may then be swiftly and accurately determined for anycontaminated sylvite.

It is noted that throughout this specification, the term impure material"is used to refer to any mixture of crude oil (or any impurity) andsylvite, or, as discussed previously, any impurity and any material,regardless of the percentage of crude oil to sylvite (or impurity tosylvite or material).

First, a sample is taken of the impure material, such as the recoveredsylvite, in which the concentration of impurity (such as crude oil) isdesired to be determined. This sample is preferably dried, such as byair drying, and, if visibly oily, as for example, more than 0.3 percentby weight after analysis, as will be discussed further hereinbelow, asmall amount, such as mg., is taken from the sample, diluted and mixedwith exactly 3 times its weight of pure, dry-200 mesh sylvite (i.e., 300mg.), or a 3:1 dilution. If, however, the sample visually appearsmoderately oily, as for example, more than 0.15 percent oil afteranalysis, a small portion thereof, as for example 200 mg., is taken,diluted, and mixed with an exactly equal weight of pure, dry, -200 meshsylvite, i.e., 200 mg. or a 1:1 dilution. If, of course, the samplevisually appears quite clean, i.e., less than 0.15 percent oil afteranalysis, no dilution is necessary.

Second, approximately 400 mg. of the undiluted sample, or all of thediluted sample, is ground until the sample is completely powdered. Thesample is now ready for pressing. For example, a 400 mg. sample may bepressed into approximately three to five thin discs. Of course, in allof the foregoing discussion, a sample of any impure material that can bepressed into flat discs after being powdered may be used with suitabledrying means necessary to obtain a usable sample disc.

Referring now to the apparatus of FIG. I, a die 10 is shown having abase portion 11 and an upper portion I2 adapted to rest on base portion11. An O-ring 13 is disposed on base portion 11 and slidably fits intoupper portion 12. A bore 14 is disposed centrally of upper portion 12. Aplunger 15 is disposed in bore 14 and an O-ring 16 is disposed on adownwardly and inwardly tapered portion 17 of upper portion 12 as can beseen in FIG. I.

A flat die or pressure pallet 18 is placed in bore 14 adapted to rest onthe uppermost face of lower portion 11 within bore 14. Preferably, thepallet 18 has its polished side facing upwardly. The sample, now apowder I9, is placed above pallet 18 and evenly distributed over theupper face thereof, as by lightly shaking die 10. This distribution maybe completed by inserting plunder l5 and rotating plunger 15 a few timesby holding it against power 19 with light pressure. The plunger. 15 isthen withdrawn slowly, so as not to disturb powder 19, and the surfaceof the powder 19 preferably should be smooth without cracks or pits. Asecond pallet 20, having its polished surface down, is then droppedabove powder I9 and pressed lightly with plunger 15.

It can be seen in FIG. 1 that a die chamber containing powder 19 isfonned between upper portion 20 and lower portion 18 ofdie l0.

The die is now placed in any suitable pressing device such as aconventional press 22, and a pressure of approximately 10 tons is put ondie 10 through suitable actuating means (not shown) coupled to press 22and left thereon for approximately 2 minutes then released.

The press 22 and lower portion 11 of die 10 is removed and, referringnow to FIG. 2, the die 10 is inverted and supported on plunger restingon surface 23. A ring 24 or the like is then placed on the bottom ofupper portion 12 of die 10 in the well 25 formed therein as can be seenin FIG. 2. Well 25 conforms to the general upper configuration of lowerportion 11 as can be seen by a comparison of FIGS. 1 and 2. Ring 24 isso configured that its outer wall abuts the inner wall 26 of well 25 ofupper portion 12.

Pressure is now slowly applied to plunger 15, as by gently pushing downon upper portion 12 of die 10, until plunger 15 moves upwardly throughbore 14 into ring 24 ad indicated by arrow 27 in FIG. 2. Such pushing iscontinued until the lower pallet 18 and powder 19 (now a pressed disc28) clear upper portion 12. The disc 28 may now be removed from die 10by any suitable means without manual handling, as, for example, bytweezers.

The disc 28 so obtained by the above method is approximately 0.015 inchin thickness (i.e., generally between 0.010 inch and 0.020 inch). Ifnot, the amount of powder 19 used should be corrected and a second discpressed. An infrared spectrum of disc 28 is preferably taken within 2hours after pressing.

Any conventional infrared spectrometer may be used to carry out thesubsequent tests, as for example, the Beckman IR-4 Spectrophotometer,Catalog No. 6800, manufactured by the Beckman Instruments, Inc. Thefollowing is a suggested method for operating the IR-4 Spectrophotometerusing the disc or discs 28 obtained in the foregoing steps set forthwith respect to FIGS. 1 and 2.

Operating Procedure for the Beckman IR-4 Spectrophotometer 1. Themachine is preferably left in the ON" position with AUTO in, the periodswitch at 32, and the COARSE GAIN on 1.

2. For 0.0 to 0.5 percent oil on sylvite analyses (for higher percentageanalyses, see note following step 5 hereinbelow):

a. The GLOWER ADJUSTMENT knob is turned on. b. The GLOWER CURRENT is setat 0.6 amperes, after a 1 minute warmup with the GLOWER ADJ UST- MENTknob.

The SCALE SELECTOR is set on 0-100.

The FINE GAIN is set a 4.00 percent.

The COARSE GAIN is set on 10.

The beam pointer is set on db. (Double Beam).

The PERIOD is set on 2 (fastest).

The SLIT CONTROL is set on SELECTOR.

The programmed slit schedule is set by adjusting SLIT WIDTH at 1.75 mm.at 14.00 microns using the knurled wheel marked SLIT.

j. The pushbutton console is used to select the scanning speed. A speedof 0.5 is normally used.

k. The desired starting wavelength is set with WAVELENGTH. For routineanalysis, a scan between 4.0 and 3.0 microns is taken. The chart isadjusted os that the scan starts on a heavy line (see FIG. 3 which showssample spectra for IPM Crude Oil on IMC Sylvite). (IPM InterprovincialMix Canadian crude oil from the Interprovincial Pipeline, while IMCInternationale Minerals and Chemical Corporation).

. The chart is engaged.

's-e w en m. A disc 28 is placed in one of the holders and both holdersare put in the machinethe sample going in the beam nearest the scantable.

n. With the WAVELENGTH" set at 4.0 microns, and the disc 28 in place,the reference beam attenuator is moved into the reference beam until therecording pen reads between 8.5 and 9.0 on the chart scale.

0. To begin scanning, the button marked SCAN is punched.

p. The scan is stopped at the desired wavelength by push ing the STOPbutton.

q. After each scan, the disc 28 is removed and its thickness measured to0.0001 using a precision thickness micrometer (marked divisions of 0.001or smaller). The sample number, dilution factor as discussed above, andthickness of each disc 28 is recorded on the strip chart (see FIG. 3).

r. A new disc 28 is put in place and the scanning procedure is repeateduntil the paper is filled or the disc samples are exhausted. Thus, ascan be seen in FIG. 3, reading from left to right, three tests of discsamples are recorded, 38, 3A and 2A, the sample having dilution ratiofactors as indicated and disc thicknesses of 0.0200, 0.00142 and 0.0163,respectively, as recorded in step q.

s. When through scanning, the GLOWER ADJUST- MENT knob is turned off andthe COARSE GAIN is set on 1 and the PERIOD is set on 3 32.

NOTE: If the sylvite contains more than 0.5 percent w. oil, a FINE GAINof 4.00 percent may not be sufficient. To check this, it is necessary togo through Step (n)and note the final reading on the chart scale. TheFINE GAIN is unlocked and set at 2.0. The beam pointer is switched to SB(Single Beam). The FINE GAIN is adjusted until the chart reading is thesame as before switching to SB; the chart reading is noted. The machineis switched back to db. and the FINE GAIN is set at the whole numbernearest twice the value noted while on SB (e.g., while on SB, if theFINE GAIN reads 2.8 -twice this is 5.6; The FINE GAIN is set on 6.00).Then, proceed with step (0 Numerical Evaluation of the InfraredSpectrum 1. An artificial baseline (B) is drawn from the point where thepeak appears on the spectrum to the point where the baseline resumes(see FIG. 3).

2. A line is drawn through the center of the largest peak and extendedto the baseline. This point is the base point 10. 3. A line is drawnacross the top of the peak this is the peak height I. 4. Using Beerslaw, the absorbance is equal to the log of the ratio between the basepoint and the peak height (A log l /lsorbance, A is calculated anddivided by thickness:

A log I /lXl lthickness Absorbance, A, is recorded on the spectrumchart.

EXAMPLE Base point: 68.30 Peak height: 62.4 Thickness: 0.0163 inchDilution: None 5. Absorbance is converted to percent by weight oil. For

IPM CRUDE OIL on IMC SYLVITE, the conversion formula is: percent w.=(0.0l27l A)0.0l 185. The conversion graph shown in FIG. 4 may be usedfor IPM Crude Oil on IMC Sylvite.

EXAMPLE absorbance was linear (see FIG. 4). A least squares" straightline for the 21 points is shown in FIG. 4. The formula is: per- 32; iiabove cent w. oil (0.0127 IX optical absorbance) 0.0l I85. Stan darddeviation (68 percent confidence level error) is i003 percent w.=(0.0l27l 2.4l8)-0.0l l85=0.029 percent w.

6. If the sample was diluted, the percent oil must be corrected for thisdilution. If diluted 1:], percent oil is multiplied by 2; if 3:l, by 4.No correction is needed if no 5 percent w.

Because of its strong absorption the carbon-hydrogen stretch band at 3.4microns was chosen. Sylvite has no peaks in this region. Separatecalibrations must be made for different d'hmon was used crude oils andfor difi'erent sylvites because of differences in 7. The results arerecorded. their spectra 1 claim as my invention: EXAMPLE 1. In a methodfor determining the purity of sylvite trans- (using sample No. 3A fromFIG. 3) ported by pipeline in an oil slurry and subsequently recovered(From the Infrared Spectrum) Base point: 64.8 from the oil, the methodcomprising the steps of:

Peak Height: 47.5 Thickness: 0.0142 taking an infrared spectrum of saidsylvite; Dilution: 3:] making up a calibration curve from knownstandards of said A log 64.8/47.5 X1/0.0l42#). l 3481X l/0.0l429.494 oilon said sylvite using a curve peak corresponding to the percent w.=[(9.4940.0l27l) 0.01l85] 4=0.l088 4 carbon-hydrocarbon stretch bands atapproximately 3.4

=0.435 percent w. microns wavelength; In summary, the calibration curvefor [PM crude oil on IMC comparing the hydrocarbon peaks appearing insaid insylvite in FIG. 3 was plotted from master samples whose totalfrared spectrum with said calibration curve; and oil content was knownfrom carbon and hydrogen analyses. determining the hydrocarbonconcentration in said sylvite Two sylvite master samples containing 1.82percent w. and from said comparison. 0.32 percent w. total oil wereblended with toluene-extracted 2. The method of claim 1 wherein the stepof taking an inand thoroughly dried sylvite to make a series of sixdifferent frared spectrum of said sylvite includes the steps of: samplesof varying oil content. The toluene-extracted sylvite taking a sample ofsaid sylvite in which the concentration of was prepared by multipleextraction of sylvite recovered from oil is desired to be determined; aprepilot plant for sylvite/crude oil separation. Recovered, drying saidsample; rather than natural sylvite, was used because the recoverygrinding said dried sample until substantially all of said processchanges the spectrum of sylvite slightly; the infrared dried sample issubstantially completely powd r spectrum method of our invention asdisclosed hereinabove is placing the powdered sample in a die chamber atatintended for recovered sylvite samples. The toluene-extracted sphericpressure; and ylvite ontained 0,04 er ent w. oil by carbon-hydrogenanalpressing at least one disc having a thickness between about i 0.01inch and 0.02 inch from said powdered sample.

3. The method of claim 2 wherein the step of drying said sample includesthe step of adjusting the dryness of said sample until the concentrationof oil in said sample is less than about 0.15 percent by weight.

The spectra of FIG. 3 was run for each of the six samples 3 three times.This produced 18 points; data was also included from two spectra of thetoluene-extracted sylvite sample and one spectrum of a hearth-driedsylvite sample. For these 21 points, the graph of total oil content(percent w.) vs. optical

1. In a method for determining the purity of sylvite transported bypipeline in an oil slurry and subsequently recovered from the oil, themethod comprising the steps of: taking an infrared spectrum of saidsylvite; making up a calibration curve from known standards of said oilon said sylvite using a curve peak corresponding to thecarbonhydrocarbon stretch bands at approximately 3.4 microns wavelength;comparing the hydrocarbon peaks appearing in said infrared spectrum withsaid calibration curve; and determining the hydrocarbon concentrAtion insaid sylvite from said comparison.
 2. The method of claim 1 wherein thestep of taking an infrared spectrum of said sylvite includes the stepsof: taking a sample of said sylvite in which the concentration of oil isdesired to be determined; drying said sample; grinding said dried sampleuntil substantially all of said dried sample is substantially completelypowdered; placing the powdered sample in a die chamber at atmosphericpressure; and pressing at least one disc having a thickness betweenabout 0.01 inch and 0.02 inch from said powdered sample.
 3. The methodof claim 2 wherein the step of drying said sample includes the step ofadjusting the dryness of said sample until the concentration of oil insaid sample is less than about 0.15 percent by weight.